C :

#include <stdio.h>
#include <stdlib.h>
int main()
{
	int i,j,n,t,a[1001]={0};
    n=20;
    for (i=1;i<=n;i++)
		scanf("%d",&a[i]);
    for (i=1;i<=n-1;i++)
     for (j=i+1;j<=n;j++)
     {
		if (a[i]>a[j])
        {
			t=a[i]; a[i]=a[j]; a[j]=t;
        }
     } 
    printf("%d",a[1]); 
    for (i=3;i<=n;i=i+2)
		printf(" %d",a[i]);
    printf("\n");
	return 0;
}

C++ :

#include<bits/stdc++.h>
using namespace std;
int main(){
	int a[25];
	for(int i=1;i<=20;i++){
		cin>>a[i];
	}
	sort(a+1,a+1+20);
	for(int i=1;i<=20;i+=2){
		cout<<a[i]<<" ";
	}
	return 0;
}